Candice Willmer's illusions can be impossible to separate from reality because every sense the victim has tells him it's all real.

Induced Hallucination is a specialization some telepaths use to interfere with the visual cortex of another, forcing them to see whatever the telepath wants them to see. Unlike light-induced illusions, the induced hallucinations force the victim to see or feel something that does not exist by interfering with the visual cortex, rather than by bending light. Because the brain cannot distinguish these phantom signals from real sensory perception, the victim is completely incapable of distinguishing illusion from reality.

Even though the DNA Alternate can force the victim to perceive whatever they choose, they have difficulty maintaining such illusions in multiple victims. The Alternate may or may not be able to control more than the visual sense, and if not, the victim would be able to deduce that the illusion is not real. Induced hallucinations are easily pierced by telepaths, who can detect the influence of the Alternate trying to deceive them.